When you use HMRC’s self-assessment online tax return, it automatically works out how much you’ll need to pay them.
After adding your figures and checking everything is correct, you can view your calculation – this shows the amount you’re due to pay for this tax return & will include income tax, class 4 National Insurance contributions and Class 2 National Insurance contributions if they’re due.
If the amount of income tax and class 4 National Insurance is more than £1,000 you must make a payment on account. A payment on account is made twice a year on the 31st of January and the 31st of July to help you spread the cost of each year’s tax. Each payment is half of your last income tax and class 4 National Insurance bill & these payments are taken off the amount you’re due to pay for the following year.
If you’d like to see how the figures have been worked out in more detail, just select ‘View and print your full calculation’ – this shows your income personal allowance tax due class 4 National Insurance Class 2 National Insurance and the total of any payments due.
Unhelpfully though, these estimated payments don’t include any payments you’ve already made so you can print a copy of this for your own records. You can find more information about self-assessment on gov.uk